The flags member contains just one flag,
IOFUNC_MOUNT_32BIT.
This flag indicates that offset in the OCB, and nbytes
and inode in the attributes structure, are 32-bit.
Note that you can define your own flags in flags, using any of
the bits from the constant IOFUNC_MOUNT_FLAGS_PRIVATE.

The conf member contains the following flags:

IOFUNC_PC_CHOWN_RESTRICTED

Indicates if the filesystem is operating in a chown-restricted
manner, meaning if only root is allowed to chown a file.

IOFUNC_PC_NO_TRUNC

Indicates that the filesystem doesn't truncate the name.

IOFUNC_PC_SYNC_IO

Indicates that the filesystem supports synchronous I/O operations.
If this bit isn't set, the following may occur:

As with the connect and I/O functions tables, the nfuncs member should be
stuffed with the current size of the table.
Use the constant _IOFUNC_NFUNCS for this.

The ocb_calloc and ocb_free function pointers can be filled with
addresses of functions to call whenever an OCB is to be allocated or deallocated.
We'll discuss why you'd want to use these functions later when we talk about extending OCBs.

Of device numbers, inodes, and our friend rdev
The mount structure contains a member called dev. The attributes structure contains two members: inode and rdev. Let's look at their relationships by examining a traditional disk-based filesystem. The filesystem is mounted on a block device (which is the entire disk). This block device might be known as /dev/hd0 (the first hard disk in the system). On this disk, there might be a number of partitions, such as /dev/hd0t177 (the first QNX filesystem partition on that particular device). Finally, within that partition, there might be an arbitrary number of files, one of which might be /hd/spud.txt.